Planets around other stars

Many evolutionists have long hoped to find evidence of life in space. They reason
that if life evolved on Earth, then it could have evolved elsewhere.1

If, as the argument goes, there are countless planets throughout the universe that
have formed via natural processes, there must be other Earth-like planets. Many
think that finding such a planet outside our solar system would be almost like finding
evidence of life in space.

Scientists have searched for years for planets orbiting other stars. These are called
extrasolar planets, or ‘exoplanets’. Astronomers first obtained evidence
suggesting extrasolar planets around 1995 while studying the sun-sized star 51-Pegasi.2 Today there are research teams
around the world searching for extrasolar planets with greatly refined research
techniques. There are now over 450 objects catalogued in exoplanet lists.3,4

Biblical perspective

The hypothetical disk of gas and dust tends to dissipate too fast for the resulting
planets to become as large as they are observed to be.

Creationists need to answer two main questions regarding exoplanets. 1) Do they
exist? and 2) How did they form? The first question has to do with experimental
evidence, but the second has to do with origins science. Scripture does not tell
us whether other stars have planets, so we must apply the best observational science
we can to answer the question.

On the other hand, Scripture is clear that God supernaturally created the earth
and the universe in four consecutive, normal-length days and that the universe is
relatively young.5 Thus,
if the observational evidence for exoplanets is sound, which I believe it is (see
box), creationists will differ with secular scientists about
how and when they formed, not whether they exist.

The Origin of Exoplanets

As scientists came to the conclusion that extrasolar planets exist, they faced challenges
in explaining their origin. From a creation point of view, it is most likely that
God created exoplanets on Day 4 of Creation Week, along with the luminaries, and
He could have created them with any characteristics He wished. Our own solar system
is special because of Earth—our system and our planet are designed to be a
safe and stable environment for life. Isaiah 45:18 acknowledges this, “He did not create
it [Earth] to be empty; he formed it to be inhabited.”

Exoplanets: enemy of evolution

There are significant scientific problems with attempts to explain the formation
of stars and planets from clouds of gas and dust.6,7 One main issue
is that the hypothetical disk of gas and dust tends to dissipate too fast for the
resulting planets to become as large as they are observed to be. There are other
major problems:

Migrating planets

Many extrasolar planets orbit extremely close to their stars—even closer than
Mercury is to the sun. Thus they are far too hot for many materials to condense
and pull together by gravity. A few exoplanets even lose matter to the star or from
their gases being essentially “boiled away”.

To address this problem, evolutionary astronomers proposed that planets could form
far away from the star and then the orbit could move inward. This is referred to
as orbit migration. This would allow the planets to form in a cooler region
of their stellar system, but then the orbit would shrink, due to friction from the
dust disk slowing the planet, to put the planet where we see it now.

The idea can also be applied in other ways. For example, in our own solar system,
astronomers realize that there would have been too little material at the distance
of Uranus and Neptune to form these giants, so they proposed that they formed closer
to our sun, then migrated outward to their current orbits.8

Orbit migration theories have difficulties because the dust disk around the star
tends to dissipate before the planet can grow large enough or before it can come
to its observed position.9

Reversed and slanted orbits

A new problem for planet origin theories has surfaced in recent months. A technique
has been developed to determine a planet’s orbital tilt relative to the equator
of the star. Several exoplanets actually have retrograde orbits10—in the opposite direction of the star’s
spin. Other exoplanets have very large orbital inclinations (slants), some more
than 80 degrees.

These strange orbits create a serious problem for planet origins models because
a planet is said to get the momentum for its orbit from the dust disk that it formed
from. Thus planet orbits should initially be in the same plane as the equator of
the star, and in the same direction as the star’s rotation. But there is no
plausible way that a dust disk can give rise to a planet with an orbital tilt of
80 degrees, let alone a reverse direction orbit.

We must not confuse an Earth-sized planet as being a truly Earth-like planet. It
is no accident that Earth is in the so-called ‘habitable zone’ in our
solar system—a narrow range of distances from the sun where liquid water can
exist.

Evolutionary planetary scientists are generally trying to answer this by assuming
that where the planet orbit is highly inclined or retrograde, there was once one
or more other planets (or possibly stars) in the stellar system that were also at
highly inclined orbits. If there are multiple objects (stars or planets) in various
highly inclined orbits, then this could possibly cause some complex orbit changes.11 Some scientists believe
that where there are three or more stars and planets in a system, it is possible
for a planet’s orbit to become highly inclined. But this must assume that
objects once existed in these systems at large distances from their star, which
we cannot or do not observe (and where did they come from?). It is also questionable
that this highly unlikely process could happen for all the known cases of retrograde
planets.

Implications

Certainly extrasolar planetary systems differ from our solar system. They show that
God created variety in the universe and that our own planet was created with design
and purpose. Astronomers are getting closer to being able to detect an Earth-sized
planet. But we must not confuse an Earth-sized planet as being a truly
Earth-like planet. It is no accident that Earth is in the so-called “habitable
zone” in our solar system—a narrow range of distances from the sun where
liquid water can exist.

No known extrasolar planets are considered habitable—lifeless Venus and Mars are more ‘Earth-like’. In
fact, even if a planet very much like Earth were eventually discovered, with an
appropriate atmosphere and liquid water, that does not in and of itself mean that
life could evolve on such a planet. We depend on our Creator for the planet we have
and to create and sustain life.

1. Doppler or radial velocity method

Astronomers measure very precisely the spectrum of the star’s light. An extrasolar
planet can cause a periodic change in the motion of the star as it orbits, essentially
making the star wobble and causing tiny variations in the colour of the light,13 due to the Doppler effect.14 If a planet is more
massive or it is close to the star, then it causes a larger “wobble”
on the star than if it were smaller or farther away. Planets that are farther away
from their stars cause slower wobbles because the planets orbit more slowly.15 Astronomers have used this
technique to discover many exoplanets and sometimes multiple planets. But while
the Doppler method can estimate a planet’s mass and distance from its star,
it can’t tell us the planet’s composition.

2. Transit or photometric method

This measures the slight drop in a star’s brightness as a planet passes in
front of it. This won’t work for most stars, because the planet must block
Earth’s line of sight. (Transit measurements have revealed exoplanets orbiting
about 100 stars.) The silhouette of a planet transiting a star gives the planet’s
size and the star’s light skirting the planet can indicate the composition
of any atmosphere.

Many of the exoplanets studied this way seem to be large gaseous planets like Jupiter
or Saturn in our own solar system. Combining a planet’s diameter with the
estimate its mass gives its density. There is at least one known case of an exoplanet
that has a similar density to Earth.16
A significant portion of this planet’s mass must be rock.

If the transit dimming of a star is in time with wobbling, this is especially strong
evidence for a planet.

3. Direct imaging

In recent years, telescopes have been launched into space to obtain photographs
of extrasolar planets as they orbit their stars. In 2009, NASA launched the Kepler
Mission, a space observatory designed for very precise transit measurements of extrasolar
planets.

One photographed exoplanet orbits a nearby star called Fomalhaut. Called Fomalhaut
b, it orbits just inside a dust ring.17
The Hubble Space Telescope took photos over two years, showing that this object
was in motion around the star. The Spitzer Space Telescope has also detected infrared
radiation from two hot Jupiter-like exoplanets.18

Direct imaging is likely to discover more exoplanets, and to verify claims from
the other methods.

Spencer, W., The Origin and History of the Solar System,
in: Walsh, R.E., ed., Proceedings of the Third International Conference on
Creationism, pp 513–523, Creation Science Fellowship, Inc., Pittsburgh,
PA, 1994. Return to text.

For example, for one exoplanet, WASP-18b, estimates suggest
the planet should have fallen into the star in about 650,000 years after formation,
much less than the presumed evolutionary age of billions of years.
Another problem is, how could the dust disk last long enough to move the planet
several Astronomical Units from the cold region where it formed to close to the
star where it is observed today? See Spencer, W.,
The search for Earth-like planets, Journal of Creation24(1):72–76,
2010. Return to text.

When the star is moving towards us, the light is ‘blue-shifted’,
i.e. to a shorter wavelength, and when it’s moving away, we see a ‘red
shift’. Return to text.

This may seem difficult to believe, but our own Sun actually
wobbles as it moves through space as well, due to the gravitational pull of Jupiter
and the other planets. Boss, Alan, Looking for Earths: The Race to Find New Solar
Systems, pp 8–9, John Wiley & Sons, Inc., New York, 1998.
Return to text.

The creationist astronomer Johannes Kepler
(1571–1630) discovered that the square of the planet’s period is proportional
to the cube of its distance from the sun, Creation15(1):40–43,
1992 creation.com/kepler. Return to text.

COROT discovers smallest exoplanet yet, with a surface to
walk on, European Space Agency News, 3 February 2009, www.esa.int. But
no one is really likely to walk on it, since its temperature is between
1000 and 1500°C! Return to text.

Kalas, P. et al., Optical images of an
exosolar planet 25 light-years from Earth, Science 322(5906):1345–1348,
28 November 2008. Fomalhaut, in the constellation Piscis Australis (‘Southern
Fish’), is only 25 light years from earth, so is one of the brightest stars
in the Southern sky. Return to text.

Naeye, R., Exoplanets: The heat is on, www.skyandtelescope.com/news,
23 March 2005. ‘Hot Jupiters’ are giant planets orbiting very close
to their star. They also noted that the infrared radiation dimmed when the planet
disappeared behind the star. Return to text.

Reader’s comments

I’m so grateful for this website! I am taking college physical science and my teacher today said that they have discovered over 4,000 other planets … but that’s a secular, worldly view and I wondered what Christian scientists had to say about it. Thank you for answering my question!

So how is it determined if a star has multiple planets orbiting around it? A star that has multiple planets would have to respond differently to the presence of those planets. And what happens when a planet never blocks the Earth’s line of sight?

To answer the second question first, if an extrasolar planet never blocks Earth’s line of sight, then it is impossible to do a transit measurement to get information about the planet. That would limit the kind of measurements that could be done.
For the first question, evidence for multiple planets orbiting a star normally comes from use of the Doppler method. If there is one planet orbiting the star, it makes a rather simple periodic variation in the velocity of the star as it moves toward or away from Earth along our line of sight. The Doppler or radial velocity method measures how much the stars velocity is changed by the planet. If there are two planets, the variation in the stars velocity is a more complicated curve. For two planets, the velocity curve would have two periodic variations superimposed. The curve would have two periods of variation. Astronomers would make observations of the red-shift usually over a period of years and develop mathematical models based on the system having one planet, two planets, three planets, etc. Then the observations of the stars velocity are fitted to the mathematical curves to see which type of planet arrangement fits the data best. If the planets all make a significant change in the stars velocity there is more confidence in concluding the planets are there. Some cases of exoplanet discoveries have been questioned when the planet is small or far from the star. In some cases, mistakes have been made and scientists have concluded that what they thought was there actually was an error. Usually Doppler measurements of newly discovered extrasolar planets are confirmed by a second research team.

Hello and may God bless this ministry. With respect to the “transit” evidence for exosolar planets, could this not also be caused by sunspots (starspots?) moving across as the star revolves? I have often wondered about this but have not seen it discussed.

“Starspots” or other variations from the star itself do have to be ruled out. This is why astronomers normally make observations of the star for years so they can get enough measurements to be confident that what they are seeing is a planet. A spot or other change in the stars light would be relatively brief and would not make a predictable periodic change in the stars light like a planet does. There may also be ways of determining how fast a star spins and this can help rule out effects like this.

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